1. Field of the Invention
This invention pertains to rail switches for track-guided vehicles. More particularly, the invention pertains to a system for switching rails that directs a track-guided vehicle along alternate paths by positioning alternate connector tracks to form alternate paths for the vehicle. The alternate connector tracks are fixed relative to one another and pivot about a single pivot point relative to main tracks on which the vehicle operates. When rotated to alternate positions, the respective connector tracks define alternate preselected paths on which the vehicle will travel.
2. Description of the Prior Art
Rail switching devices are well known in the art. The primary objectives of devices disclosed in the art have typically been to provide efficient and reliable switching operations and smooth operating surfaces, and to minimize space requirements for the operation and storage of a switch. A typical rail switch provides a path for a vehicle to traverse along a main line, and upon operation of the switch, activates engagement with a secondary or branch line path onto which the vehicle is diverted. Upon a reverse operation of the switch, the track is reconfigured to again provide a path along the main line over which the vehicle can operate.
The prior art discloses four basic methods of switching: sliding, roll-over, lateral translation, and swinging. U.S. Pat. No. 4,109,584 illustrates switching by sliding. The patent provides for switching by sliding two separate sections of tracks at the switching location. The patent teaches this two part switching mechanism to avoid the great weight of a single switch of the size required. The patent recognizes that an even larger number of switch components or segments would reduce the weight per segment further. However, the patent also recognizes that such a configuration would require a more intricate control device that would unnecessarily complicate the apparatus. The '584 patent thus reached a compromise with the two segment design.
U.S. Pat. No. 5,499,583 discloses a rail switching apparatus that rolls over about the longitudinal axis of the main line of track. The primary advantage cited by the patent is to shelter certain electrical components of the apparatus when the apparatus is in alternate positions. However, because the apparatus rolls 90.degree. about its longitudinal axis and deposits the unused portions of the switch below the portions of the switch in use, the rail switch also discloses an efficient use of lateral space. Disadvantages of the switch are that it requires a greater than typical amount of vertical clearance, and it requires that a heavy center track section be supported for rotation. Additionally, the rail switch requires hinged outer track sections that must be displaced by the switch when the switch is operated to complete the operation. Thus, when the switch is operated, the outer section of the track not in use must be swung about its hinge out of position. These track hinges are additional operable parts that further complicate the apparatus.
U.S. Pat. No. 4,970,965 discloses a similar roll-over switch. The mechanisms and liabilities of the switch are essentially similar to the operation and liability of the switch disclosed in the '583 patent. However, the rail switch of the '965 patent does not hinge the outer sections of track as the '583 patent discloses. No hinge is required because all of the switching track section are rolled over to perform the switching operation. Additionally, the switch of the '965 patent rolls 180.degree. rather than 90.degree. as disclosed in the '583 patent.
A laterally translating switch is shown in U.S. Pat. No. 5,657,696. The switch is designed to provide the required switching while moving the track to alternate angles of bank. While the design does effectively meet its goal of providing switching positions with appropriate bank, it is not an ideal switch in several other respects. For example, because a whole track section must be both lifted and arcuately moved laterally, a significant vertical clearance is required. Also, a relatively large amount of energy is required to both lift and translate. Moreover, the design requires that the combined track assembly twist and bend as it is moved from one switching position to the other. Such a requirement necessarily causes wear and fatigue of the switch assembly.
A further method of switching rails is by swinging the appropriate switching components into and out of position. U.S. Pat. Nos. 4,993,326, 4,919,055, and 4,016,818 disclose different types of swinging switches. The '326 patent shows a single swinging piece that is hinged to a main line of the system and alternately swings back and forth under the action of the switch between the main line and a branch line. The '055 patent provides a similar arrangement except that the hinge includes partial main line and branch line track segments that are swung or pivoted between operable and inoperable positions to make the desired connection. The '818 patent also discloses hinges to both the main line and the branch line and has two separate rail sections that provide alternate paths upon activation of the switch.
Each of these swinging switches provides hinges on the paths of travel of the vehicles traversing the lines. The hinges therefore necessarily provide obstacles around which the traversing of a vehicle along the lines must be designed. For a vehicle that has wheels that wrap around the rail, such obstacles are unacceptable. The '818 and '055 patents disclose an apparatus that is hinged at multiple locations. Such designs add complexity to the switching mechanism by providing multiple bearing and rotation points that must be installed and maintained.
It is therefore obvious that none of the switches in the prior art provide a rail switching apparatus that is compact, efficient to move, easily maintainable, and quickly operable. Nor does the prior art provide an apparatus that is positively lockable and that makes use of hinge or pivot points clear of the operable track such that the hinges do not interfere with the operation of certain vehicles traversing the track.